This invention relates generally to sheet holding tray cassettes for photocopy machines, and particularly to cassettes with upwardly biased lift plates on which sheets are stacked to be fed into the photocopier.
Many photocopy machines provide for paper to be supplied to the machine from removable trays. The trays are generally filled outside the machine and are then inserted into the machine where they cooperate with feeding elements for transporting the sheets into the photocopier. The sheet feed discharge position in the photocopier is ordinarily substantially fixed. The feeding elements generally act on the top sheet of the paper stack, and the position of the top sheet must be maintained as sheets are discharged from the tray and the size of the stack decreases. Thus, the stack must be raised in some way, in a fairly continuous manner, to maintain the same vertical position of the top sheet of the stack.
One common way to maintain a constant discharge position is to support the paper stack on a lift plate that is spring biased upwardly. In a tray cassette, the lift plate may be upwardly pivotable about its rear edge in response to springs disposed between it and the bottom plate of the tray. Importantly, the spring constant of the springs is chosen so that the top of the stack, whether full or substantially empty, remains generally in the same vertical position.
When a spring loaded tray cassette is filled with a sheet material, the spring force urging upward the lift plate on which the stack is placed must be overcome. This can be both awkward and inconvenient, especially if the spring force is large. Thus it may be inconvenient to load the paper so that it lies in a properly aligned position beneath, for example, the corner separators.
Accordingly, it is an object of the invention to provide a tray cassette with an upwardly biased lift plate, on which sheets are stacked, that is convenient to load. Other objects are to provide such a tray cassette that has a minimum of additional mechanical parts, and that operates in conjunction with the photocopier frame to minimize the mechanical operations that an operator must do in loading the cassette.